International travel is turning the world into one giant supercontinent — and that's a very dangerous thing

Every year, millions of people travel across the planet in boats,
trains, cars, and planes. Along with them often travel dozens of
tiny hitchhikers — foreign plants, insects, and sometimes other
animals too.

These introduced species have colonized the globe from South
Africa to Antarctica.

As a result, writes, Kolbert, "global diversity — the total
number of different species that can be found worldwide — has
dropped."

Barring any immediate changes in our actions, the diversity is
slated to continue declining. Eventually, scientists predict, we
will have succeeded in reshuffling the life on the planet to such
an extent that, from a biological perspective, the terrain will
start to look virtually identical — no matter where you are.

"From the standpoint of the world's biota, global travel
represents a radically new phenomenon and, at the same time, a
replay of the very old," Kolbert writes.

In other words, we're reversing what happened when the continents
that once made up Pangaea gradually drifted apart.

This, writes Kolbert, is "another way in which humans are running
geologic history backward and at high speed. Think of it as a
souped-up version of plate tectonics, minus the plates."

By transporting plants and animals from one corner of the globe
to another, Kolbert writes, "we are, in effect, reassembling the
world into one enormous supercontinent — what biologists
sometimes refer to as the New Pangaea."

In the New Pangaea, many of the plants and animals we're familiar
with today won't exist. They will have been
killed off by invaders.